Heretofore, as a water discharge valve device for a flush water tank configured to store therein flush water for flushing a toilet bowl, and a flush water tank assembly equipped with the water discharge valve device, there has been known a type which comprises: a casing provided to surround a discharge port formed in a bottom of a flush water tank and a water discharge valve for opening and closing the discharge port; an opening formed in a peripheral wall of the casing; and a valve element for opening and closing the opening of the casing, as described, for example, in the following Patent Document 1.
In this conventional type of water discharge valve device and a flush water tank assembly equipped therewith, when full toilet bowl flushing (full flushing mode) is performed, the water discharge valve is moved upwardly (lifted) to open the discharge port, while maintaining the opening of the casing in its open state, to thereby cause flush water in the flush water tank to pass through the opening of the casing, so that an amount of flush water to be discharged from the discharge port to the toilet bowl is increased. On the other hand, when partial toilet bowl flushing (partial flushing mode) is performed, after closing the opening of the casing by the valve element, the water discharge valve is moved upwardly to open the discharge port, so that the amount of flush water to be discharged from an inside of the flush water tank to the toilet bowl via the discharge port is reduced. In this way, it is possible to switch to either one of the full flushing mode and the partial flushing mode.